BPEL File Structure

The topmost structure of a BPEL executable process can include the elements shown in Listing 7.3 and also can include a BPEL extension element (<extensions>), which is used in relation to other technologies such as Service Component Architecture.

Listing 7.3: BPEL process elements

 <process>    <import> </import>    <partnerLinks> </partnerLinks>    <messageExchanges> </messageExchanges>    <variables> </variables>    <correlationSets> </correlationSets>    <faultHandlers> </faultHandlers>    <eventHandlers> </eventHandlers>    <!- The previous two elements include activities,       as does the subsequent content of the process       element. Activities can be enclosed in scopes,       as described later. -> </process> 

Here are highlights of a process definition:

• Each import provides access to a WSDL definition or an XML Schema.

• Each partner link is a kind of specialized variable that describes the relationship between the BPEL process and a partner service.

• Each message exchange is an identifier that is used to avoid an ambiguous case in a complex business scenario - specifically, to pair a BPEL activity that receives a message with the activity that issues a reply.

• Each variable contains business data, whether to hold a message or for other use in the process logic.

• Each correlation set is a listing of properties used to correlate service instances.

• Each fault handler is a set of activities that run in response to a fault, which is a failure in the process.

• Each event handler is a set of activities that run concurrently with other activities, in response either to the passage of time or to receipt of a message.